--- self[nth]=val

    nth ܤǤ val ꤷޤnth 
    ϰϤۤˤĹưŪ˳ĥĥΰ
    nil ǽޤ

    val ֤ޤ

--- self[start..end]=val

    start ܤǤ end ܤǤޤǤ 
    val Ƥִޤval ͤǤʤȤˤ 
    val ִޤval Ǥο¿ˤϡ
    Ǥޤ

    val  nil   [] ʤ start  
    end ޤǤǤޤ

    :

        ary = [0, 1, 2, 3, 4, 5]
        ary[0..2] = ["a", "b"]
        p ary

        # => ["a", "b", 3, 4, 5]

        ary[2..4] = nil
        p ary

        # => ["a", "b"]

    val ֤ޤ

--- self[start, length]=val

    ǥå start  length ĤǤ 
    val Ƥ֤ޤval ǤʤȤˤ 
    val.to_ary ⤷ [val] Ƥִޤ
    val ֤ޤ

    :
        ary = [0, 1, 2, 3]
        ary[1, 2] = ['a', 'b', 'c']
        p ary                        # => [0, "a", "b", "c", 3]
        ary[2, 1] = 99
        p ary                        # => [0, "a", 99, "c", 3]
        ary[1, 0] = ['inserted']
        p ary                        # => [0, "inserted", "a", 99, "c", 3]

